1. Field of the Invention
The present invention relates generally to cementless total hip arthroplasty and, more particularly, to an improved press-fit femoral stem prosthesis.
2. Related Art
In recent years, cementless total hip arthroplasty has enjoyed significant clinical success. To date, the design of press-fit femoral stem prostheses has focused on providing a tight fit within the metaphyseal portion of the femur to eliminate the potential for relative motion. Prior art femoral stem prostheses generally have a circular or rectangular cross-sectional shape and end abruptly in a blunt tip distally. While some of the prior art femoral stem prostheses have achieved the desired tight fit, two major problems remain associated with press-fit stems: the occurrence of thigh pain and abnormal femoral bone remodeling.
It is now believed that the thigh pain and femoral bone remodeling which occur with prior art press-fit femoral stem prostheses result from stem stiffness and the concentration of bending stress at the distal tip of the implants. Since bone tissue will remodel in direct relation to the stress applied to it, it is desirable to equalize the application of stress over the length of the femur following implantation of the prosthesis to avoid bone resorption in some areas and hypertrophy in other areas. Unfortunately, due to their mechanical stiffness, prior art femoral stem prostheses stress-shield the proximal end of the femur, leading to bone resorption in this region. Stress transfer occurs primarily at the prosthesis/bone interface at the blunt distal end of prior art prosthetic stem designs, leading to bone hypertrophy in this region.
It is an object of the present invention to eliminate the thigh pain and to decrease the bone remodeling which occur with other press-fit stems.